1. Field of the Invention
This invention relates to the field of video signal processing, and particularly to a system for encoding a video signal with digital information such as a time code, tape location information or recorded program identification.
2. Background Art
When recording a video signal, it is often desirable to encode the video signal with a time code or other digital information. A time code is particularly useful for providing an accurate reference for locating specific segments of the recorded signal. In this way, for example, a videotape may be edited by designating the starting and ending times of those portions of the video signal that are to be retained in the edited copy. Magnetic recorders for professional use will often dedicate a track on the recording medium for recording a time code, but no such track is provided in the popular VHS recording format used in nearly all home video recorders.
A dedicated time code track requires that the time code information, generally in the form of digital data, be magnetically recorded on the same medium as the audio and/or video signal. To utilize the time code, it would be necessary to provide dedicated record and playback heads for the time code track. Due to the added complexity of recording and decoding magnetically recorded time codes, such capability is unavailable in consumer products.
Another approach used in professional recording equipment is a vertical interval time code (VITC). Standards for VITC have been established by the Society of Motion Picture and Television Engineers (SMPTE). Time coding with VITC does not require a dedicated recording track, but instead encodes timing data onto one of the non-viewed horizontal lines within the vertical blanking interval of the standard video signal format prescribed by the National Television Standards Committee (NTSC).
There are a number of situations in which time code data or some other location and/or identification information would be valuable in the home recording environment. One particular situation involves the playback of previously recorded videotapes of broadcast programs. Such "time shifting" is the most common use of home market video cassette recorders (VCR's). Most home viewers prefer to view only the program portion of such videotapes and will frequently "fast forward" through the commercial and promotional interruptions. Ideally, a system could be provided to automatically "fast forward" through such interruptions during playback of the videotape. The assignee of this application is developing such a system. The system requires a timing reference for the video signal during playback of the videotape so that previously identified portions of the signal that contain commercial and promotional messages may be scanned past at a fast rate. Such timing information may be provided in a variety of ways; however, one of the most expedient ways is to have time code information recorded on the videotape itself.
Another example of a situation in which recorded time code information would be useful in the home market is in editing home videos. Just as in the professional field, editing of home videos may be facilitated with accurate time code information encoded directly on the tape.
Since home market VCRs do not provide the dedicated recording and playback heads nor the associated circuitry for time coding a recorded signal, there is a need for an alternative way of obtaining accurate timing information for a recorded video signal. Moreover, it would be highly desirable to provide such a capability without modifying conventional VCRs or videotapes.